This application claims the priority of Korean Patent Application No. 2004-22887, filed on Apr. 2, 2004, in the Korean Intellectual Property Office, the contents of which are incorporated herein in their entirety by reference.
1. Field of the Invention
The present invention relates to signal measurement and, more particularly, a measurement circuit and method for analyzing differential signals generated by a semiconductor device or system.
2. Description of the Related Art
Recently, a high-speed serial data interface has become a standard data interface in mobile application products. Through the high-speed serial data interface, serial data composed of differential signals are transmitted between a personal computer and a liquid crystal display monitor or between a personal computer and a universal serial bus (USB) 2.0 at a high transmission rate. The differential signals used in the high-speed serial data interface include a differential plus (DP) signal and a differential minus (DM) signal. When a transmitting side transmits transmission data in the form of the differential signal, a receiving side extracts the transmission data from a signal obtained by subtracting the DM signal from the DP signal. This is for the purpose of preventing the transmission data from being affected by noise using the fact that the signal obtained by subtracting the DM signal from the DP signal has no noise because the DM signal is simultaneously affected by the noise when the DP signal is affected by the noise.
Among high-speed serial data interface application products, the USB 2.0 is being widely used for mobile applications. When a semiconductor device such as the USB 2.0 is manufactured, “compliance tests” with respect to only some standardized items including a receiving function, transmission jitter, crossover voltage, rising time and falling time are carried out due to various difficulties in tests. In a high speed mode for transmitting 480 MHz data, the differential signals are probed and measured. In a full speed mode for transmitting 12 MHz data, single-ended signals with respect to DP and DM signals are probed and analyzed in a semiconductor device such as the USB 2.0.
FIG. 1 shows signal waveforms displayed by a general measuring instrument, and FIG. 2 is an eye diagram of the two signals of FIG. 1 when the signals are merged in parallel by the general measuring instrument. The general measuring instrument such as an oscilloscope can show two signals, that is, DP and DM signals, probed by a device under test (DUT), such as USB 2.0, simultaneously, as shown in FIG. 1. Furthermore, the general measuring instrument can merge the two signals in parallel to show the merged signal in the eye diagram, as shown in FIG. 2. The eye diagram of FIG. 2 is a signal waveform obtained by dividing the signals of FIG. 1 at a specific period and overlapping the divided signals. The state of the signals shown on the oscilloscope is analyzed through the eye diagram. That is, a degree of jitter in the probed signals is analyzed from the signal waveform of the eye diagram. From portions (A) and (B) of the eye diagram of FIG. 2, a crossover voltage at which a rising edge and a falling edge meet is analyzed. Furthermore, the rising time and falling time of the signals can be known from the rising edge and falling edge of the eye diagram.
In the semiconductor device such as the USB 2.0, a test of full-speed mode single-ended signals can be easily analyzed by the general measuring instrument such as the oscilloscope, as described above. However, the test analysis cannot be carried out in an environment where the test is executed by automated test equipment (ATE). When automated test equipment (ATE) is used, data corresponding to a difference signal between DP and DM signals is stored in a predetermined memory and a test of a high speed mode is analyzed through the stored data. In this case, however, single-ended signals for a full speed mode test cannot be simultaneously shown on a display. Accordingly, a signal test using the eye diagram of the single-ended signals cannot be easily carried out.